Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

518
FXUS63 KLOT 191054
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
554 AM CDT Fri Jun 19 2026

.KEY MESSAGES...

- Rain showers will likely pass through the area tonight.
  Isolated thunderstorms and locally gusty winds may also be
  observed in a few areas this evening.

- There is potential for heavy rainfall and thunderstorms in the
  region on Sunday, though whether these threats will
  materialize here locally remains uncertain.

&&

.DISCUSSION...
Issued at 316 AM CDT Fri Jun 19 2026

Today through Saturday:

The daytime hours today will be dry and will feature plenty of
sunshine courtesy of a ~1016 mb surface high drifting just to
the southwest of our area. Today`s high temperatures should end
up being a few degrees warmer compared to yesterday with mid-
upper 70s temperatures advertised across most of our forecast
area in our official gridded forecast database, though would not
be surprised to see a few 80 degree readings here and there
based on some of the latest bias-corrected temperature guidance
output. That said, temperatures within a few miles of the
lakeshore in Illinois and slightly farther inland in northwest
Indiana will remain a bit cooler this afternoon behind a lake
breeze.

This evening, a well-defined upper-level shortwave diving into
the Dakotas from Saskatchewan early this morning will reach our
longitude. The shortwave may be in a somewhat weakening state as
it begins to shear out, but coupled with modest low to mid-
level frontogenesis and cold frontal/outflow-driven forcing at
the surface, there should be enough forcing for ascent present
for rain showers to spread into northern Illinois and northwest
Indiana from the northwest as this wave arrives. Mid-level lapse
rates will be far from exceptional, but should nevertheless be
steep enough to support some potential for charge separation and
isolated lightning strikes within any deeper convective
updrafts/wherever lift is maximized. Surface dew point
depressions on the order of 20-30 degrees and 50+ kts of mid-
level flow could also support gusty winds in excess of 30 mph
with any deeper convective elements or immediately behind any
consolidated gust fronts this evening, but the lack of more
appreciable instability should preclude a threat for stronger
wind gusts from materializing.

While a few showers may still be ongoing near the lingering
frontal zone in our southern counties come sunrise Saturday
morning, conditions are expected to dry out across the entirety
of our forecast area by midday. High temperatures tomorrow look
to be fairly similar, if not a smidge warmer, compared to
today`s highs, though post-frontal onshore flow should keep some
of our northwest Indiana locales a bit cooler relative to
elsewhere.


Sunday:

The most notable upper-level disturbance progged to track
through our region over the next seven days will eject eastward
out of the central Rockies on Saturday and reach our neck of
the woods on Sunday, accompanied by an attendant surface low.
Ensemble guidance over the past few days has struggled to get a
good handle on how this ejecting shortwave disturbance and
associated surface low will evolve, and this theme has continued
with the latest 00Z ensemble suite. The existing and persisting
ensemble variance can partly be explained by slight differences
in the configuration of various influencing synoptic-scale
features this weekend, but it is also a likely byproduct of the
extensive coverage of convection that is expected across the
central Plains on Saturday and what effects that may have in
modulating the main synoptic wave and surface low. Because of
the role that this central Plains convection may play in
dictating the strength and track of the shortwave and surface
low, their ultimate evolution will likely not be truly known
until Saturday night at the earliest, once observational trends
with the Plains convection have become apparent (and even then,
there`s no guarantee that the system`s track and strength will
become obvious). Despite the existing uncertainties, there is
fair agreement across the ensemble suite that this system will
track over or close enough to our area for at least part, and
quite possibly all, of our CWA to see rain from it on Sunday, so
made no changes to the 70-90% PoPs delivered by the NBM.

Model guidance generally favors precipitable water values
peaking anywhere between 1.25" and 2" here, which raises concern
for notable rainfall rates that could bring about some
potential for flooding. Whether such a threat for flooding will
ultimately materialize here, though, appears to be contingent
upon either 1.) a relatively strong surface low developing and
tracking across or just south of our forecast area and inducing
a robust deformation band on its northern flank that steadily
pumps out rainfall at a good clip as it persists over the same
areas for a few hours, and/or 2.) the surface low tracking far
enough to the north for the associated warm front, richer
boundary layer moisture (70+ degree dew points), and greater
instability to enter our forecast area, allowing for
convectively-driven torrential rainfall rates to occur with any
thunderstorms that develop near and south of the front. Will
also note that the latter scenario would also introduce a
potential for severe weather for at least our southern counties
on Sunday. The envelope of the latest ensemble and deterministic
forecast guidance shows mixed support for both of these
scenarios, but there are also several advertised outcomes with
relatively weak surface lows and more southerly surface low
tracks that would make this a relative non-event for our area
with fairly insignificant rainfall totals and little to no
thunderstorm activity north of I-74. The bottom line right now
though is that, while a great deal of uncertainty remains,
Sunday continues to be a day to monitor for potential weather
impacts in our area, so stay tuned for forecast updates.


Monday through Thursday:

After the Sunday system clears the region, quieter and drier
conditions should settle into the area for the beginning of the
upcoming work week. However, there remains a signal for another
upper-level disturbance embedded within northwesterly flow aloft
to bring another round of precipitation to the area sometime in
the late Tuesday through Wednesday time frame. Global ensemble
meteograms are otherwise in relatively good alignment on
temperatures remaining near to below normal for this time of
year through at least the middle of the upcoming week.

Ogorek

&&

.AVIATION /12Z TAFS THROUGH 18Z SATURDAY/...
Issued at 554 AM CDT Fri Jun 19 2026

There are no significant aviation weather concerns anticipated
through the period.

West-northwest winds will prevail at most terminals through the
period as surface high pressure shifts eastward across the
Lower Missouri Valley today. The only exception to this being at
KGYY, where winds look to turn north-northeasterly off the lake
for a period this afternoon in association with a lake breeze.
It appears unlikely that this lake breeze will shift far enough
inland to impact ORD and MDW. Diurnal mixing of the boundary
layer may result in some gustiness up to near 20 kt this
afternoon, but any gustiness will quickly abate into early this
evening. Otherwise, expect VFR conditions to prevail today.

The next weather impulse will track southeastward into the
western Great Lakes into this evening. As it does, we should see
an increase in VFR cloud cover and a chance (~50%) for a period
of light showers this evening. The only change for the 12z TAFs
was to transition the PROB30 mention to a tempo group for a few
hours this evening. The threat of lightning continues to look
low with this activity.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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